The present invention relates to a pump and more particularly to a rotary blade pump in which the pump characteristics and the ability of the blades to shift relative to the pump body are improved.
Hitherto, for example, as disclosed in U.S. Pat. No. 3,187,679 of F. Scognamills, the pump means rotary pump shown in FIGS. 1 and 2 of the attached drawings has been publicly known. In these drawings reference numeral 1 designates a bracket of an electric motor (not shown), reference numeral 2 designates a rotary shaft of this motor journaled in the bracket 1 by a bearing 3, and reference numeral 4 designates a rotor splined to the rotary shaft 2 concentrically, the rotor 4 radially shiftably receiving a number of blades 5 (the number being three in this embodiment) respectively within radial slots formed therein. Reference numeral 6 designates a cylindrical housing the inner periphery of which has a center line disposed eccentrically with respect to the center line of the rotary shaft 2 and of the rotor 4, and reference numerals 7 and 8 designate suction and discharge ports, respectively, formed in the housing 6 substantially at opposite sides of the rotor 4.
The operation of the pump means shown in FIGS. 1 and 2 is as follows.
Upon rotation of the rotary shaft 2 in the direction indicated by the arrow in FIG. 2, the blades 5 driven together with the rotor 4 are caused to protrude radially outwards by the action of centrifugal force so that they displace with their radially outer peripheries into abutment with the inner periphery of the housing 2 while radially shifting relative thereto, whereby the air within a vacuum tank (not shown) is sucked through the suction port 7 and discharged through the discharge port 8. In this manner, a pumping action takes place in a manner well known in the art.
However, since it is usual in the pump means of this kind that each blade 5 is constituted from a material having an abrasive quality such as carbon, graphite, or the like, the end surfaces 5a and 5b at the extreme longitudinal ends of the blades 5, which confront and carry out a shifting movement relative to the confronting surfaces of the housing 6 and the bracket 1, are subject to abrasion, the bracket 1 and housing 6 being made of aluminium, pig iron, or the like. This results in a decrease in pump performance and deterioration of the ability of the blades to shift relative to the bracket 1 and the housing 6 owing to their jamming, and in extreme cases even the locking of blades may occur.
For the purpose of providing a non-lubricated blade for a pump means of this kind there is disclosed in Japanese Laid-Open Utility Model Publication No. 161611/1979 a blade in which the basic portion is made of a thermosetting resin containing inorganic or organic substances as a filler, and the surface portions such as the side surfaces confronting the slot formed in the rotor and the radially outward peripheral surface coming into contact with the inner peripheral surface of the housing are formed from a material which has excellent wear resistance and a low coefficient of friction. However, in this blade no consideration is given to the end surfaces 5b and 5a at the extreme longitudinal ends of the blade 5 which shift relative to the bracket and the housing during pump operation.
Further, in this prior art, since the side surfaces of the blade to be shifted relative to the slot formed in the rotor and the radially outward peripheral surface thereof to be shifted relative to the inner peripheral surface of the housing are formed from a material having a superior wear resistance and a low coefficient of friction:
(i) the inner peripheral surface of the housing and the side walls of the slot of the rotor relative to which the blade shifts are worn; and
(ii) the function as a solid lubricant by the powdered graphite, carbon, etc. generated as the result of the wear of the blade which is usually made from those materials does not occur because of the coating of the graphite, etc. with the wear resistant material.
Contrarily, as will become apparent later, in the present invention, since the blade has only its longitudinal ends coated with a material having a superior wear resistance:
(i) the wear of the parts relative to which the blade shifts is decreased;
(ii) the powdered graphite, carbon, etc. can effectively function as a solid lubricant because of the wear of the other parts of the blade; and
(iii) the pump operation is assured owing to the lack of wear of the longitudinal ends of the blade. (Even if the parts of the blade other than the longitudinal ends wear, the pump operation is not affected since the blade is urged radially outwards due to centrifugal force.).